The present invention relates to a method and an apparatus for detecting a defect in an image on a display screen, that is, a pixel having a higher or lower luminance than the other pixels.
One example of a method for detecting a jammed shadow mask of a color cathode-ray tube (CRT) is described in JP-A-63-42454 "Method for checking a Shadow Mask on a CRT". This method is designed to detect a jammed shadow mask based on the difference between an original image and an image where shadow mask holes are shifted from the original image by one pitch.
The foregoing prior art operates to check for an abnormal shadow mask based on an original image and another image where shadow mask holes are shifted from those of the original image by one pitch for the purpose of detecting a jammed shadow mask hole on a color CRT. This arrangement makes it difficult to obtain a difference in signal level between a normal portion and an abnormal portion output from an imaging camera if a hole suffers from a slight abnormality, thereby being making it substantially impossible to realize stable detection. Further, the prior art operates on the assumption that no relative inclination exists between the imaging camera and a CRT to be checked. Hence, the prior art has a disadvantage that it is quite difficult to offset the adverse effect of the inclination.